You're absolutely right! However, as you said, it solves the user's problem from their point of view.
The main reason I started this project was that other dyndns alternatives (whether they be proxies or "fully-fledged" operations) have rather ugly domain names, in my opinion. 'zzzz' popped into my head, I saw that 'zzzz.io' was free, and decided to get it. A few weeks later, I finally got around to throwing a webapp together so others could benefit.
Not such a horrible thing to do, or?
And yes, the service is backed up by Amazon's Route 53. I did learn a thing or two about BIND and DNS from the experience though, which is also a plus.